We have shown that the newborn PV muscle has a longer relaxation time than the adult, possibly contributing to the higher PV resistance observed early in life. Since K+ channel activation has been implicated in the control of PV resistance, we compared the effect of 2 K+ channel blockers: 4-AP and Barium upon the stress (mN/mm2) and relaxation time (s) of NB and adult rabbit pulmonary artery muscle (PAM). The Pulmonary artery was stimulated with Phenylephrine to obtain stress, and the 1/2 relaxation time was measured after electrical stimulation. Results: The NB PAM stress was 5±1.2 and significantly lower (P<0.05) than the adult (8.8±1.5). The relaxation time was 34±4 in the adult and 419±179 in the NB(P<0.01). K+ channel blockers had no effect on the adult. In the NB a relaxation time reduction to the adult levels and a tendency for a decreased stress was observed (Figure). We conclude that K+ channel blockade has a developmentally distinct effect upon the rabbit PA and speculate that early in life, either increased activation or greater sensitivity of the K+ channels may account for the developmental differences in the relaxation properties.

figure 1